This disclosure relates to novel compositions of matter based upon a nanocomposite comprising aerogel components and polymeric components. Embodiments relate generally to imaging members, and specifically to components of imaging members that provide electrical and mechanical functions and that comprise such nanocomposites.
In some typical imaging systems, toner images are electrostatically transferred to a relatively thin intermediate belt in a plurality of first transfer nips. The images are then electrostatically transferred in a second transfer nip to a hot transfuse member, such as a transfuse belt. The intermediate belt heats up after passage through the second transfer nip. However, prior to the first transfer nip, the temperature of the intermediate belt is cooled and maintained at a stable temperature condition. In this manner, the imaging system is “buffered” from the transfuse heat. The images on the transfuse belt are then Theologically transferred to paper in a third transfer nip.
Some components, such as bias charging rollers, bias charging blades, bias transfer rollers, transfix belts, transfuse rollers and belts, and bias transfer belts provide electrical, thermal, and mechanical functions in such conventional imaging systems. These components are typically made from composites of particle-filled, for example metal or carbon particle-filled, and/or ionic salt-filled, elastomeric materials. The polymers and certain of the filler materials generally included in these composites are typically hydrophilic. The components made from these hydrophilic composites have an affinity for water and can absorb from about 1 to 12 percent by weight of moisture upon immersion in liquid water or exposure to high humidity environments, and can, upon drying, desorb an equivalent amount of water. This absorption-desorption cycle is generally reversible and results in the swelling and shrinking of the composite in response to changes in environment and relative humidity. The subsequent change in mass and physical dimensions of a solid part made from these hydrophilic composites leads to a humidity expansion coefficient that can be unacceptably large, for example between 1.05 and 1.15. Such a large humidity expansion coefficient may, in turn, result in unwanted swelling and shrinkage of tightly mated components, such as for example, slip-fit assemblies. In addition, poor reliability and shortened useful lifetimes of components may result, because critical properties of the components, such as physical dimensions, electrical conductivity and mechanical modulus, may be instantly and adversely affected by environmental conditions, particularly in cases in which the components must cycle between cold, dry and hot, wet environments.
For example, typical ionic-salt filled elastomer components may have altered bulk and/or surface resistivity due to water that has absorbed onto and/or diffused into the material. Composites such as those used in conventional bias transfer rolls, for example, consist of a quaternary ionic salt in a soft, polyester type polyurethane resin system. Such conventional composites, particularly in the form of elastomeric foams, can absorb about 5 to about 12% by weight of water as the environment changes from a dry condition, such as less than about 10% relative humidity, to a wet condition, such as more than about 90% relative humidity. This water absorption may alter the electrical or the mechanical properties of the composite. For example, the addition of water to an elastomeric composite can decrease the electrical resistivity by more than an order of magnitude. Volume resistivity, which measures the ability of the material to pass electrical current under the influence of a direct current (d.c.) electric field, is an intrinsic property of the composite. Changes in resistivity occur because of the absorbed water's actions within the composite. For example, water occupies space, which simultaneously swells the polymer and increases the mobility of charge carriers within the space defined by the solid volume of the composite, and thus decreases resistivity. Water can also solubilize ionic salts, producing more charge carriers, which, in turn, can further decrease resistivity. The presence of water within the composite can also soften the polymer, decreasing, for example, the mechanical modulus and hardness of the composite and thereby increase the composite's stress relaxation and creep tendencies. These effects can cycle as a function of the changes in the local environment and cause undesirable fluctuations to these properties and to the performance of the composite in its intended application.
Alternately, the polymers and selected fillers may be hydrophobic, meaning that the composites made therefrom have a weak affinity for water and are likely to absorb only relatively small amounts of water or water vapor when exposed to a high humidity environments. While it is generally desirable to select hydrophobic polymers and fillers for applications requiring environmental stability, there is a need for more and lower cost materials options.
Efforts have been made to control and/or compensate for the adverse effects of environmental changes by using moisture barrier coatings on effected components. In addition, constant current power supplies and/or constant force nip-forming mechanisms are often used to compensate for local environmental variations. However, failures still occur because critical component properties may change in response to variations in temperature and humidity, especially over long periods of time.
Thus, there remains a need for materials having stable electrical and mechanical properties, with which to make components that perform both electrical and mechanical functions in imaging systems.